OK, let's try again. I have an old MB seatbelt unit that I hope is similar to yours. Pull the belt all the way out to expose the very end, which is looped around the spindle, in the slot on the upper side in pic1, around the spindle, and out the lower slot. The picture shows the vice grips holding the spring-loaded spindle (actually the rachet disk, one on each side).
If off the car, you might have to hold the bar away from the rachet to be able to pull the belt out, like on a come-along.
Take your screwdriver and push in on the end of the belt in the lower slot and pry the belt out of the slot. As shown in pic2, the belt is sewn into a loop with the steel rod inserted in the loop to keep it in place. It's very tight in the slot because of the double thickness of the sewn loop.
To remove, take the rod out, and work the belt out of the spindle slots. Insert the new belt into the slot, work it out of the other slot, reinsert the rod and pull the sewn end and rod snuglt into the spindle slot.
Hope this helps.
